There is no automated backup or history of deleted scenes in OBS. You have to use the general backup application you use for your machine. In case you don't have such, this is the moment where you should think about starting to use one. The most simple backup is the File History feature that comes with Windows. It's already installed. You just have to grab some external storage (USB or NAS) and activate File History. See Windows Settings->Update & Security->Backup.